[LTP] [PATCH v2 18/33] keyctl26: Test KEYCTL_DH_COMPUTE size query

[Andrea Cervesato <andrea.cervesato@suse.de>]

From: Andrea Cervesato <andrea.cervesato@suse.com>

Test KEYCTL_DH_COMPUTE buffer size query: verify that calling
with buflen 0 returns the required output buffer size (256)
without writing to userspace.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 runtest/syscalls                            |  1 +
 testcases/kernel/syscalls/keyctl/.gitignore |  1 +
 testcases/kernel/syscalls/keyctl/keyctl26.c | 53 +++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+)

diff --git a/runtest/syscalls b/runtest/syscalls
index 1b059f652..108efa4a8 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -743,6 +743,7 @@ keyctl22 keyctl22
 keyctl23 keyctl23
 keyctl24 keyctl24
 keyctl25 keyctl25
+keyctl26 keyctl26
 
 kcmp01 kcmp01
 kcmp02 kcmp02
diff --git a/testcases/kernel/syscalls/keyctl/.gitignore b/testcases/kernel/syscalls/keyctl/.gitignore
index 4cf772558..dd282b7ce 100644
--- a/testcases/kernel/syscalls/keyctl/.gitignore
+++ b/testcases/kernel/syscalls/keyctl/.gitignore
@@ -23,3 +23,4 @@
 /keyctl23
 /keyctl24
 /keyctl25
+/keyctl26
diff --git a/testcases/kernel/syscalls/keyctl/keyctl26.c b/testcases/kernel/syscalls/keyctl/keyctl26.c
new file mode 100644
index 000000000..32bc5f393
--- /dev/null
+++ b/testcases/kernel/syscalls/keyctl/keyctl26.c
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Andrea Cervesato <andrea.cervesato@suse.com>
+ */
+
+/*\
+ * Test ``KEYCTL_DH_COMPUTE`` size query of :manpage:`keyctl(2)`.
+ *
+ * [Algorithm]
+ *
+ * - verify calling ``KEYCTL_DH_COMPUTE`` with ``buflen = 0`` returns required
+ *   buffer size (256) without writing
+ */
+
+#include "keyctl_common.h"
+#include "keyctl_dh_data.h"
+
+static struct keyctl_dh_params *dh_params;
+
+static void setup(void)
+{
+	SAFE_KEYCTL(KEYCTL_JOIN_SESSION_KEYRING, 0, 0, 0, 0);
+
+	dh_params->priv = new_user_key("dh_priv", dh_priv, sizeof(dh_priv),
+				       KEY_SPEC_PROCESS_KEYRING);
+	dh_params->prime = new_user_key("dh_prime", dh_prime, sizeof(dh_prime),
+					KEY_SPEC_PROCESS_KEYRING);
+	dh_params->base = new_user_key("dh_base", dh_base, sizeof(dh_base),
+				       KEY_SPEC_PROCESS_KEYRING);
+}
+
+static void run(void)
+{
+	TST_EXP_VAL(keyctl(KEYCTL_DH_COMPUTE, (unsigned long)dh_params,
+			   (unsigned long)NULL, 0, 0),
+		    (long)sizeof(dh_expected_secret));
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.test_all = run,
+	.min_kver = "4.7",
+	.needs_kconfigs = (const char *[]) {
+		"CONFIG_KEYS=y",
+		"CONFIG_KEY_DH_OPERATIONS=y",
+		"CONFIG_CRYPTO_DH",
+		NULL
+	},
+	.bufs = (struct tst_buffers []) {
+		{&dh_params, .size = sizeof(*dh_params)},
+		{},
+	},
+};

-- 
2.51.0


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